The Research On High Efficient Utilization Of The Phase-change Thermal Storage Solar Water Heating System In Residential Buildings

Renewable sources,such as solar energy has attracted more attention as energy consumption in buildings increases.As an important part of solar thermal utilization,increasing the efficiency of solar water heating system is of great significance to solve the energy problem.Centralized solar water heating system has a good prospect for development in residential buildings because of its unique advantages,but the low guarantee rate is one of the problems exposed during the usage of it.Combination of phase-change materials and solar water heating system in a suitable package can improve the system guarantee rate and promote the application of solar collector system.This paper analyses the centralized heat collection and distribution of solar hot water system in residential building and determines the final form of direct storage of hot water tank by comparing the five forms'system characteristics.Paraffin wax was chosen as the experimental material.The phase change tank adopts the spherical phase-change unit stacking form,and the material of the phase change unit,the diameter of the unit and the thermal conductivity of the phase change material are optimized by the experimental method,finally we determined the diameter is 60mm,the material is stainless steel,filling the paraffin wax and adding the graphite powder to strengthen the heat exchange.Then a phase-change thermal storage solar water heating system was set up.In order to compare the effect of different phase transition temperature materials,the phase transition temperature of 55 degrees and 60 degrees were selected to test the heat storage,heat release and thermal insulation properties of the phase change water tank.The thermal storage experiment was carried out to simulate the performance of phase change water storage in different solar irradiance conditions.In the exotherm experiment,the heat release between the temperature control mode and the following control mode was compared,and the actual heat release performance of the water tank was also investigated.In addition,this paper calculated the guaranteed rate of the phase change thermal storage solar water heating system taking the maximum daily demand of the user as the demand of the system.The experimental results show that the phase-change material can complete heat storage in 2-4.5 hours at 10.8 MJ/m~2,15.1 MJ/m~2 and 19.4 MJ/m~2 solar irradiance.The exothermic rate of the 60 degree phase-change material was 83%and the 55 degree phase-change material was 78%in the exothermic experiment.Temperature difference control mode is suitable when there is low user occupancy rate or the total daily heat demand is not high,while the follow-up control mode is suitable for a case where the occupancy rate is high or the heat fluctuation is large.According to the typical annual meteorological parameters of Tianjin,the same energy situation,the solar energy guarantee rate of without adding the phase-change water tank system was about 53%in operation(March-October).The solar energy guarantee rate of the 55 degree phase-change water tank system was about 79%and the solar energy guarantee rate of the 60degree phase-change water tank system was about 83%,which is 26%-30%higher than that without adding the phase-change water tank system.The research results not only show that phase change materials can significantly improve the solar energy guarantee rate in centralized heat collection of solar hot water system,but also play a certain role in preventing overheating and enhancing the guarantee ratio of rainy days.